1. Field of the Invention
This invention relates to media for optically recording and reproducing information.
2. Related Background Art
Heretofore, magnetic materials have been mainly used as materials for recording media, for example, credit cards, floppy disc, etc. Magnetic recording media are advantageous in that writing and reading of information can be readily carried out, but are problematic in that the recorded information can be readily altered and high density recording cannot be carried out. In order to solve these problems and efficiently handling various kinds of information, methods for optically recording information with an optical recording medium have been proposed In this connection, optical recording media, recording and reproducing systems, recording and reproducing apparatus, etc. have been also proposed. For example, an optical recording medium having a recording layer comprising a gelatin matrix and silver particles dispersed in the gelatin matrix has been proposed as a medium for optically recording and reproducing information. Furthermore, heat mode recording material which can record information by spotwise irradiating a recording layer containing the recording material with an energy beam such as laser beam, etc., thereby partially changing the state of the recording layer has been also proposed. These recording materials require no developing treatment after the writing of information, and thus provide DRAW (direct read after write) media, which are expected to have applications as disc or card recording materials due to their high density recording capability and their information adding capability.
A film comprising an organic coloring matter whose physical properties can be changed with light of relatively long wavelength is free from the aforementioned problems, is non-toxic and can be formed by coating, that is, at a low product cost. Thus, applications of the film to an optical disk or card have been extensively studied and proposed.
Optical recording media now used in offices, for example, optical disks, etc. generally have a hollow structure, but pocketable optical recording media, for example, optical cards are desirably made as thin as possible. Although a tightly sealed structure is desirable for this purpose, the tight sealing leads to the following problem.
In case of the optical recording layer comprising an organic coloring matter, a material used in a bond layer laid on the recording layer for bonding it to a protective substrate may chemically attack the recording layer, resulting in a decrease in the recording contrast and a failure in information reproduction.
The optical recording media used in offices are preserved at constant temperature and humidity or encased with jackets, whereas pocketable optical recording media are actually exposed to severe service conditions, for example, severe temperature and humidity conditions, and also have many chances for bending, resulting in occurrence of peeling at the bond layer.